Normoglycemic environment is important for the growth and function of islet isografts

Beneficial Effects of Hyperbaric Oxygen Therapy on Islet Transplantation

We envisage that hyperbaric oxygen (HBO) would ameliorate islet anoxia, preventing early graft failure. Thus, treatment of HBO to diabetic recipients should improve the outcome of islet transplantation. We tested this hypothesis by syngeneically transplanting insufficient number of islets (150 islets) into streptozotocin-diabetic C57BL/6 mice, each followed by HBO (2.4 ATA, 100% O₂) therapy for 1.5 h from day 0 to 28, once daily (group A) or twice daily (group B), or from day 5 to 28, once daily (group C) or twice daily (group D), 6 days/week. Recipients without HBO treatment served as controls. At day 28 after transplantation, groups B, C, and D gained weight and had lower blood glucose compared with their baseline values. In addition, groups B and D had higher insulin content of the graft than the controls. To determine the optimal timing of HBO therapy, groups B and D were compared with recipients treated with HBO twice daily, 6 days/week, from day -14 to 0 (group E) and from day -14 to 28 (group F). At day 28 after transplantation, groups B, D, E, and F had significantly lower blood glucose than their individual baseline values and higher insulin content of the graft than controls. But only group F had more β-cell mass of the graft than controls. These findings lend credence to the expectation that peritransplant application of adequate frequency of HBO to diabetic recipients would enhance the performance and growth of the islet graft, resulting in an improvement of the outcome of the transplantation.

Influence of Donor Age on Mouse Islet Characteristics and Transplantation

Old donor age has been considered as a risk factor and relative contraindication for transplantation. This study was designed to investigate the influence of donor age on islet characteristics and transplantation. Islets isolated from 8 (I-A)-, 32 (I-B)-, or 64 (I-C)-week-old C57BL/6 mice were studied for number, size, insulin content, and secretion. After syngeneically transplanting 300 islets under the kidney capsule of strep-tozotocin-diabetic mice (R-A, R-B, and R-C, respectively), we measured recipients' metabolic parameters as well as the β-cell mass and insulin content of the graft. Eight-week-old donors had better glucose tolerance than 32- and 64-week-old donors. However, 64-week-old donors had more pancreatic insulin content than 8- and 32-week-old donors. I-B and I-C were greater in number, larger in size, and higher in insulin content than I-A. But perifusion study showed I-C secreted less insulin, albeit with a similar stimulation index compared with that of I-A and I-B. After transplantation, the fall of blood glucose in R-C was faster than that in R-A and R-B. At 12 weeks, the recipients' blood glucose, body weight, HbA1c, and the β-cell mass and insulin content of the graft were comparable in all groups. However, R-C had better glucose tolerance than R-A. During follow-up, R-A and R-B maintained lifelong normoglycemia and their glucose tolerance did not deteriorate. These data indicate that islets isolated from donors with different ages have different characteristics and effects on transplantation. The islets isolated from aged donors are functioning well and can be a potential source for transplantation; however, because we transplanted a large islet mass from the aged donors, the role of the islet dose needs to be further clarified.

Coculture of hepatocytes with islets

Bioartificial liver support (BAL) systems are potential new therapeutic approaches for use as liver support to prevent nutrient deficiencies, hypoxia, or ischemia before the acquisition of donated organs. To investigate whether islets are beneficial for hepatocyte function and survival, we cocultured BALB/c mouse islets with C57BL/6J hepatocytes to assess hepatocyte viability, function, and apoptosis. We observe cell viability to decrease progressively by 50% from day 0 to day 3 among isolated hepatocytes (group A) and hepatocytes cocultured with islets (group B). However, group A was prone to necrosis and reduced albumin secretion during culture. In contrast, at day 7 group B maintained albumin secretion (0.3351 ± 0.0581 vs 0.1451 ± 0.0329 μg/h/mL; P < .05). Early apoptosis was observed at day 3 among group A but at day 7 in group B. In addition, quantitative analysis of the apoptotic cells revealed group B to show a delayed phenotype of both early and late apoptosis compared with group A. Our results indicated that islets could retain hepatocyte function and delay apoptosis, suggesting that the coculture system is potentially applicable to develop a high-performance BAL.

Effects of cyclooxygenase-2 inhibitor and adenosine triphosphate-sensitive potassium channel opener in syngeneic mouse islet transplantation

In the initial days after transplantation, islet grafts may be attacked by cytokines via cyclooxygenase-2 (COX-2), producing primary nonfunction. In addition, chronic overstimulation of β-cells may impair insulin secretion. To enhance the function of transplanted islets, the present study investigated the effects of rofecoxib, a COX-2 inhibitor, and NN414 (6-chloro-3-[1-methylcyclopropyl]amino-4H-thieno[3,2-e]-1,2,4-thiadiazine 1,1-dioxide), an adenosine triphosphate-sensitive potassium channel opener, on islet transplantation. Male inbred C57BL/6 mice were used as donors and recipients. One hundred fifty islets were isolated via collagenase digestion and density gradient, and syngeneically transplanted under the kidney capsule in mice with streptozotocin-induced diabetes. Recipients were treated with or without rofecoxib, 10 mg/kg/d orally, or with or without NN414, 3 mg/kg/d orally, for 4 weeks. After transplantation, recipient body weight, blood glucose concentration, and intraperitoneal glucose tolerance were measured. The grafted kidney was extracted for determination of insulin content at 4 weeks. In the rofecoxib-treated and NN414-treated groups and both control groups, body weight remained stable, and the blood glucose concentration decreased progressively. However, at 4 weeks after transplantation in the groups treated or not treated with rofecoxib or NN414, no significant difference was observed in recipient body weight, blood glucose concentration, and glucose tolerance or in insulin content of the graft. These data indicate that posttransplantation treatment with rofecoxib or NN414 has no beneficial effect on transplantation outcome in diabetic mouse recipients engrafted with a marginal islet mass.

Magnetic resonance imaging study of mouse islet allotransplantation

Although only 10% of islet transplant recipients maintain insulin independence, 80% of them are C-peptide positive at 5 years. To better understand the fate of transplanted islets, a magnetic resonance imaging (MRI) technique has been used to detect superparamagnetic iron oxide (SPIO)-labeled transplanted islets. Recently, we successfully used a novel MRI contrast agent, chitosan-coated SPIO (CSPIO) nanoparticles, to monitor mouse islet isografts for 18 weeks after transplantation. In the present study, we tested whether CSPIO could be applied to monitor islet allografts, which are supposedly rejected without immune interventions. Male C57BL/6 and Balb/c mice were used as donors and recipients of islet transplantation, respectively. After overnight incubation with or without CSPIO (10 μg/mL), 300 C57BL/6 islets were transplanted under the left kidney capsule of each Balb/c mouse. Starting from day 10 after transplantation, 3.0-Tesla MRI of the recipients was performed weekly. Four mice were followed for ≥38 days. At 38 and 45 days, 1 islet graft was removed for insulin and Prussian blue staining, respectively. From days 10 to 45 after transplantation, CSPIO-labeled islet grafts were visualized on MRI scans as sustained distinct hypointense spots homogeneously located at the upper pole of left kidney, the site of transplantation. At days 38 and 45, the histology of CSPIO-labeled islet grafts revealed insulin and iron staining colocalized in the same areas. Our results in a mouse allotransplantation model indicated that CSPIO-labeled islets survived as long as 45 days with positive MRI.

Magnetic resonance imaging of transplanted mouse islets labeled with chitosan-coated superparamagnetic iron oxide nanoparticles

Although only 10% of islet recipients maintain insulin independence, 80% of them are C-peptide positive at 5 years after transplantation. To better understand the fate of transplanted islets, a magnetic resonance imaging (MRI) technique has been used to detect Feridex-labeled islet grafts in rodents. In this study, we used a novel MRI contrast agent, chitosan-coated superparamagnetic iron oxide (CSPIO) nanoparticles, to monitor mouse islet grafts. Male inbred C57BL/6 mice were used as donors and recipients of islet transplantation. The islet cytotoxicity was evaluated by fluorescein diacetate and propidium iodide staining for RAW cells incubated with CSPIO. After being incubated overnight with and without CSPIO (10 mg/mL), 300 islets were transplanted under the left kidney capsule of each mouse. After transplantation, 3.0-Tesla MRI of the recipients was performed biweekly until 19 weeks. At the end of study, the islet graft was removed for insulin and Prussian blue staining. The cell death rates in RAW cells did not increase with increasing CSPIO concentrations or incubation time. The grafts of CSPIO-labeled islets were visualized on MRI scans as distinct hypointense spots homogeneously located at the upper pole of left kidney. Their MRI signal was 30%-50% that of control islets and was maintained throughout the follow-up period. At 18 weeks, the histology of CSPIO-labeled islet graft revealed the insulin- and iron-stained areas to be almost identical. Our results indicate that isolated mouse islets labeled with CSPIO nanoparticles can be effectively and safely imaged by using MRI as long as 18 weeks after transplantation.

Improved glucose regulation on a low carbohydrate diet in diabetic rats transplanted with macroencapsulated porcine islets

Islet xenografts from porcine donors can reverse diabetes in experimental animal models and may be an alternative to human islet transplantation. We have recently reported the ability of porcine islets encapsulated in a double layer of hydrophilic agarose to maintain in vitro functional ability for >6 months. Although beta-cells are capable of adapting their secretory capacity in response to glucose levels, evidence has shown that prolonged hyperglycemia can compromise this ability. The aim of the present study was to determine the effects of diet manipulation on the long-term regulation of blood glucose levels, and the preservation of functional islet in the macrobeads. Twenty-one streptozotocin-induced diabetic Wistar-Furth male rats were randomly assigned to two diets containing 64% carbohydrate (CHO) or 20% CHO. Groups of five to six animals assigned to either diet were implanted with either empty (EM) or porcine islet-containing macrobeads (PIM) and followed for 333 days. Observations included general condition, body weight, blood glucose, and food and water intakes. Monthly blood samples were collected for insulin and C-peptide analysis. The 20% CHO diet significantly lowered blood glucose values when compared with those of the 64% CHO groups for both the empty (14.94 +/- 0.41 vs. 16.26 +/- 0.42 mmol/L, respectively, p < 0.001) and islet macrobead recipients (12.88 +/- 0.39 vs. 15.57 +/-0.85 mmol/L, respectively, p <0.001). The different diets, however, had no statistically significant effects on the preservation of islet mass in the macrobead. Serum porcine C-peptide was detected throughout the experiment in animals receiving porcine islet macrobeads, regardless of diet. Diabetic rats fed a low carbohydrate level diet and transplanted with porcine islet macrobeads had improved total tissue glucose disposal and improved clinical parameters associated with diabetes.

Effects of heme oxygenase-1 transgenic islets on transplantation

Heme oxygenase-1 (HO-1) has been described as a protein capable of cytoprotection via radical scavenging and apoptosis prevention. The aim of this study was to analyze whether HO-1 overexpression in freshly isolated murine transgenic islets resulted in cell protection and improved in vivo functional performance after transplantation. We produced transgenic mice in which the human HO-1 transgene driven by chicken beta-actin promoter was expressed in the heart, liver, spleen, lung, kidney, muscle, intestine, and pancreas in Balb/c mice. One hundred fifty islets isolated from HO-1 transgenic and control Balb/c mice were syngeneically transplanted under the left kidney capsule of the streptozotocin-diabetic Balb/c mice. The recipients who underwent transplantation with HO-1 transgenic islets showed higher blood glucose than those with control islets at 4 weeks (320 +/- 25 vs 189 +/- 43 mg/dL; P < .05). Body weight was not significantly different between the 2 groups. Our data indicate transgenic islets with high HO-1 expression did not improve transplantation outcome.

Effects of Insulin Sensitizers on Islet Transplantation

To solve the problems of islet engraftment, we investigated the effects of insulin sensitizers, metformin and rosiglitazone, on the in vitro and in vivo function of mouse islets. The in vitro study was done by culturing 30 isolated C57BL/6 mouse islets with glucose (100 or 300 mg/dL) or rosiglitazone (4.5 mumol/L) for 2, 4, 8, or 12 hours. The in vivo study was performed by syngeneically transplanting 150 C57BL/6 mouse islets under the kidney capsule of streptozotocin-diabetic mice. The metformin group was treated with 200 mg/kg/d in water and the control group was pair-fed the same volume of liquid diet. In the in vitro study, insulin release stimulated by 300 mg/dL glucose (n = 6) was the highest at all time points. That stimulated by rosiglitazone (n = 6) was greater than by 100 mg/dL glucose (n = 6) only at 8 hours. In the recipients treated with metformin (n = 17) and controls (n = 13), the blood glucose decreased and body weight increased gradually after transplantation. However, there was no significant difference between the two groups. Their tolerance to intraperitoneal glucose challenge at 2 and 4 weeks was also comparable. At 4 weeks, 12/17 (71%) in the metformin group and 8/13 (62%) in the control group achieved normoglycemia (P = .60). At 4 weeks, the insulin content of the graft was 8.35 +/- 3.42 mg in the metformin group and 5.28 +/- 4.28 mg in the control group (P = .59). Our data indicate that (1) rosiglitazone stimulated isolated islets to release insulin but was less effective than high levels of glucose; and (2) metformin treatment had no beneficial effect on islet recipients.

Characteristics and transplantation of the porcine neonatal pancreatic cell clusters isolated from 1- to 3-Day-Old versus 1-Month-Old pigs

Porcine neonatal pancreatic cell clusters (NPCCs) isolated from 1- to 3-day-old pigs (I-A) cured diabetic nude mice within 8 weeks after transplantation. To shorten the latent period between transplantation and reversal of hyperglycemia, we studied NPCCs isolated from 1-month-old pigs (I-B). One- to 3-day-old or 1-month-old pig pancreata were cut into fragments, digested by collagenase, and then studied for islet characteristics. In addition, 300 cultured NPCCs were transplanted under kidney capsule of nondiabetic nude mice. At 1 and 3 months after transplantation, the grafts were removed to measure the insulin content and beta-cell mass. Immediately after isolation, I-B was larger than I-A (0.211 +/- 0.006 vs 0.189 +/- 0.003 mm(2), P =.0003) and after a 6-day culture period, I-B contained more insulin than I-A (6.8 +/- 1.4 vs 2.3 +/- 0.2 microg/150 NPCCs, P =.02). However, the stimulation indices of I-A and I-B during static incubation with 500 mg/dL glucose (26.5 +/- 3.2 vs 23.9 +/- 1.7) or 500 mg/dL glucose plus 50 mol/L IBMX (41.9 +/- 4.4 vs 62.2 +/- 14.0) were not significantly different. Furthermore, neither I-A nor I-B showed first or second phase insulin secretion during sequential perifusion with 100 or 300 mg/dL glucose. In nondiabetic recipients, the insulin content of the graft at 1 month after transplantation was 0.3 +/- 0.0 and 0.3 +/- 0.1 microg, and the beta-cell mass of the graft at 3 months was 0.069 +/- 0.022 and 0.067 +/- 0.023 mg in mice receiving I-A or I-B, respectively (P >.05). Our data indicate NPCCs isolated from 1- to 3-day-old and 1-month-old pigs have different characteristics but similar transplantation effects.